27 September 1996

trouble below

Yield maps can spot

By James de Havilland

ALTHOUGH cautious about reading too much into his early yield maps, Oxfordshire farmer Philip Chamberlain has found that helping to spot subsoil problems is one area where yield mapping has proven useful from the outset.

With over 90 fields making up his 1400ha (3460 acres) of arable land, Mr Chamberlain is the first to admit he cannot recall all the patches within a given field where yields have been influenced by physical factors such as laid crops or pest damage.

It was in helping to recall where those patches were that his early use of yield maps proved useful. But other variations in yield could be attributed to panning, he thought.

"An early example was where one half of a field showed up as not doing as well yield wise as the other," says Mr Chamberlain. "As the soil type did not vary significantly across the field, and the crop was not laid or pest damaged, it followed that the differences were likely to have been caused by soil structure problems. Digging with a spade revealed a pan across the field, but it was more severe on the lower yielding half."

The farms Simba Tandem Mono cultivators suit a more planned approach to subsoiling. Comprising hydraulically adjust-able subsoiler legs mounted between front and rear disc gangs, the implement is designed to enable subsoiling depths to be hydraulically adjusted according to actual pan depths, with discing alone being carried out where subsoil problems have not been found.

"Subsoil problems have one of the greatest effects on yield," says Guy Leversha of Simba. "But subsoiling an entire field to deal with localised panning is expensive. The data from yield maps can almost provide a contour map of where a farmer should dig trial holes to find a pan, and then deal with them as necessary.

"Having a subsoiler that is hydraulically adjustable on the move will enable pans to be dealt with where they have been found, with areas that have no pan being acted on by the cultivators discs alone." Mr Chamberlain admits to having subsoiled the whole field where the pan was found. "But we could have chosen to work only the lower yielding half.

"In a catchy season having the yield map data to illustrate where the need to subsoil is greatest could save time and help make the decision of where to subsoil easier," he reckons That could also boost profits by raising yields where they are being depressed by subsoil problems.

That raises the question of whether a subsoiler could be integrated into an automated precision farming approach. Having a "controlled" subsoiler that is adjusted according to pre-programmed data sounds attractive.

But that would bring with it practical problems, not least the varying draft load imposed upon the tractor pulling the implement. A sudden increase in load, for example, could cause wheel-slip or require a gear change. Should the latter be automated as well?

Mr Leversha points out that the aim of on-the-move adjustment is to enable the operator to reset the machine from the tractor seat to deal with different pan depths, and not necessarily to vary the depth according to the imple- ments position in the field. &#42


&#8226 Possible soil problems can be identified.

&#8226 Field checks confirm.

&#8226 Subsoiling can be targeted.

&#8226 Cost and time savings in autumn.

&#8226 Yield benefits.


HOW MAPS HELP

Precision farming helps pay its way by allowing variable sub-soiling across fields on Philip Chamberlains Oxon farm. The Simba Monos hydraulically adjustable tines ease the operation.